Virgin olefin polymers modified with organic polyisocyanates



United States Patent 3,382,215 VIRGIN OLEFIN POLYMERS MODIFIED WITHORGANIC POLYISOCYANATES Bernard 0. Baum, Plainfield, N..I., assignor toUnion Carbide Corporation, a corporation of New York No Drawing.Continuation of abandoned application Ser.

No. 182,918, Mar. 27, 1962. This application July 14,

1967, Ser. No. 653,578

9 Claims. (Cl. 260-775) ABSTRACT OF THE DISCLOSURE The instantspecification discloses adhesives prepared by (1) reacting virgin olefinpolymers with organic polyisocyanates or (2) reacting virgin olefinpolymers with organic polyisocyanates and organic peroxides. Virginolefin polymers are those which have not been subjected to deliberateoxidation. The polymers of this invention may be used as coatingmaterials, films, or as laminate interlayers.

RELATED APPLICATION This application is a continuation of copendingapplication Ser. No. 182,918, filed Mar. 27, 1962, now abandoned.

This invention relates to modified olefin polymers exhibiting improvedclarity, stress cracking resistance and adhesion to a wide variety ofsubstrates. More particularly, the invention relates to a method formodifying olefin polymers to exhibit one or more of the abovecharacteristics and to olefin polymers so modified.

The term olefin polymers is used in the present specification and claimsto denote normally solid homopolymers of alpha mono-olefinicallyunsaturated hydrocarbons as well as normally solid copolymers thereof,with one or more other organic compounds copolymerizable therewith whichcontain polymer producing unsaturation, such as is present for examplein carbon monoxide and formaldehyde and in compounds containing theethylene linkage C=C e.g. styrene, vinyl stearate, butene, vinylacetate, vinyl formate, methyl acrylate, monobutyl maleate, 2-ethylhexyl acrylate, N-methyl-N-vinyl acet amide, acrylic acid, ethylacrylate, methacrylic acid, isoprene, butadiene, acrylamide, vinyltriethoxysilane, bicycloheptene, bicycloheptadiene, divinyl phosphonateand the like. Many other copolymerizable monomers which can be used inaddition to these illustrative compounds are well known to the art.Preferred olefin polymers in this invention contain at least percent byweight of a combined alpha mono-olefinically unsaturated hydrocarbonhaving from 2 to 4 carbon atoms inclusive, i.e. butene-l, propylene andespecially ethylene.

Olefin polymers are desirably modified for various end uses, forexample, to provide increased molecular weight, higher thermaldeformation temperatures, improved clarity and enhanced solventresistance. Heretofore, such modification has been carried out bycrosslinking the olefin polymer as by irradiation, or by treatment withperoxides. Peroxide crosslinking accomplishes the desired improvementsin olefin polymers but has undesirable side effects such as the leavingof residues which may adversely aifect stability, electrical andpermeability properties.

As packaging materials, olefin polymer films are characteristicallysuperior to cellulosic and metallic materials in flexibility, resistanceto tear and in being unaffected by moisture and chemically activeenvironments. Cellulosic and metallic packaging materials, however, aregenerally superior to olefin polymer films in shock-absorbing propertiesand are more easily handled in automatic packaging machinery. Acombination of the properties of these packaging materials is possibleby laminating or coating the olefin polymer on the cellulosic ormetallic material. The general inertness of the olefin polymers tosolvents and adhesives, however, has thus far substantially preventedobtaining of suitable laminated and coated substrates except by costlypretreatment of the olefin polymer surface, e.g. etching with chromicacid, subjecting to corona discharge and flame treatment.

It is an object, therefore, of the present invention to provide olefinpolymers exhibiting increased molecular weight, higher thermaldeformation temperatures, improved clarity and enhanced solventresistance and which are not reduced in stability or permeability.

It is another object to provide olefin polymers which exhibit goodadhesion to both porous and nonporous substrates without the need ofsurface treatment of the polymer after shaping which are adapted to usein coating and in laminate constructions.

It is another object to provide a method for modifying olefin polymersto impart increased molecular weight, higher thermal deformationtemperature characteristics, improved clarity and enhanced solventresistance.

It is another object to provide a method for modifying olefin polymersto impart improved adhesional characteristics.

It has now been discovered that surprising and marked adhesionalproperties are imparted to olefin polymers by reacting the olefinpolymer with a polyisocyanate, preferably a normally solidpolyisocyanate, an organic compound contatining at least two N=(h0groups.

It has further been discovered that the joint use of critical amounts ofan organic peroxide with a polyisocyanate results in a synergisticimprovement in adhesional properties of both virgin olefin polymers andoxidized olefin polymers i.e. olefin polymers having a peroxide content(measured as described below) of from 0.15 to 3.5 milligrams (mg)peroxide per gram resin and/or an infra-red carbonyl content (alsomeasured as described below) of from 0.0005 to 0.03 carbonyl absorbanceper mil resin and also improved physical properties, particularlyincreased molecular weight, higher thermal deformation temperaturecharacteristics, improved clarity and enhanced solvent resistance.

It has further been discovered that these improved physical propertiesand marked adhesional properties are imparted to hydroxyl contatiningolefin polymers by reacting with a polyisocyanate.

Important and advantageous modifications of olefin polymers can beachieved by the use of non-free-radical crosslinking agents, namelypolyisocyanates, which have heretofore been achieved only by the use offree radical type crosslinking agents e.g., peroxides. Moreover, the useof polyisocyanates as crosslinking agents poses none of the problemsassociated with peroxide crosslinking agents used alone.

A highly surprising and unexpected property of the polyisocyanatereacted olefin polymers of this invention is their marked adhesionalproperties. These olefin polymers applied as liquids for coating or asfilm for surfacing various substrates or as laminate interlayers exhibittenacious adhesion to fibrous, nonfibrous, porous, and nonporous,flexible and rigid, metallic and nonmetallic, polymeric, cellulosic andglass surfaces.

In general, the method of this invention required for impartingadhesional characteristics to olefin polymers mixing to substantialhomogenity the olefin polymer and the polyisocyanate and modifying theolefin polymer by reacting the isocyanate groups with the olefinpolymer.

In order to modify olefinic hydrocarbon polymers in molecular weight,thermal deformation temperature characteristics, improved clarity andenhanced solvent resistance, it is essential in the method of thisinvention to mix to substantial homogenity such an olefin polymer withthe above peroxide and carbonyl characteristics, the polyisocyanate andthe peroxide and erosslink the olefin polymer by reacting the isocyanateand peroxide crosslinking agents with the olefin polymer.

These peroxide and carbonyl values cannot be obtained without deliberateoxidation.

The particular means of achieving oxidation of the olefin polymer is notnarrowly critical. Broadly, intimately contacting the olefin polymerwith an oxygen containing environment such as air, oxygen, ozone,various catalytic agents, or chemical reagents for a sufiicient lengthof time will result in the oxidation production of certain isocyanatereactive groups. Among these groups are carboxyl, hydroxyl,hydroperoxide and hydrogen groups. Levels of peroxide and/or carbonylwithin the above limits are indicative of the presence of suitableamounts of these oxidation produced groups.

A suitable means of producing these groups in olefin polymers is tobubble ozone, or oxygen or a mixture thereof, e.g. 2% ozone in oxygen,through a heated bed e.g. to 60 C. of powdered e.g. 20 mesh, virginolefin polymer for a sufficient time e.g. for 60 minutes.

This treatment of a virgin ethylene homopolymer which normally has acarbonyl absorbance per mil of 0.0002 and a peroxide content of 0.04milligram per gram resin results in an oxidized ethylene polymerincreased in carbonyl absorbance to 0.003 per mil resin and peroxidecontent to 1.4 milligrams per gram resin. Also suitable is treating thevirgin olefin polymer with an oxidizing chemical e.g., by slurryingpowdered resin in heated chromic acid (sulfuric acid-potassiumdichromate) for about 30 minutes. The resin should be washed with waterafterwards to remove acid and dichromate. This treatment of virginethylene homopolymer causes an increase in carbonyl absorbance per milto 0.005 and in peroxide content to 1.5 milligrams per gram resin.

Still another suitable method of controllably oxidizing ethylenepolymers is milling the polymer in air r oxygen containing atmosphere atelevated temperatures e.g., above 110 C. for a sufficient period e.g. 45minutes. This treatment of ethylene homopolymer causes an increase incarbonyl absorbance to 0.007 per mil and in peroxide content to 1.9milligrams peroxide per gram resin. Other oxidizing means includeagitation in suitably atmospherically controlled apparatus other thanroll mills. Oxidation can also be effected by sparging oxygen, air orozone into a solution of the ethylene polymer.

From the foregoing illustrative means for oxidizing the olefin polymers,it can be seen that in any method wherein heat and oxygen are mutuallypresent with an olefin polymer under conditions insuring a good degreeof contact between the polymer and the oxygen, oxidation will takeplace. It is of course also required that the contactmg be carried outfor a time sufiicient to build up corbonyl absorbance and peroxidecontent levels to the above set forth minimal values.

By the term virgin olefin polymers is meant those olefin polymers whichhave not been subjected to deliberate oxidation by mechanical working,solvating or chemical reaction in an oxidizing atmosphere. As pointedout above, the oxidation levels needed in the olefin polymers formolecular weight, solvent resistance, clarity and thermal deformationimprovement are not present in virgin olefin polymers. Reaction orvirgin olefin polymers which have less than these oxidation levels withpolyisocyanates does not provide to a significant extent the foregoingimprovements but does impart remarkable adhesion properties. In theabsence of deliberate oxidation the oxidation level is of olefinpolymers are substantially as shown in Table I in which all percentagesare by weight and in which the carbonyl absorbance and peroxide contentwere determined as hereinafter set forth.

' It is to be pointed out that hydroxyl (OH) containmg polymers byvirtue of having these groups do not require oxidation to the prescribedlevels of peroxide content and/or carboxyl absorbance incontradistinction to polymers and copolymers of nonhydroxyl groupcontaining olefins.

Polymers and copolymers of monomers containing mixed functional groupseg hydroxyl containing carboxylated olefin monomers and carboxylcontaining hydroxylate olefin monomers can also be reacted with thepolyisocyanates of this invention with or without peroxides to impartthe herein described properties.

TABLE I Carbonyl Peroxide Olefin Polymer Absorbanee Content,

per mil 1 mgJgm. resin Ethylene homopolymer:

(0.92 density) 0. 0002 0. 04 (0.945 density) 0. 0002 0. 02Ethylene/carbon monoxide: (94%/6%) 0. 06 Ethylene/propylene: 0 035 48 '2Ola 0. 045

0. 024 (94%I6%) 0. 05 Ethyl one/vuyl acetate (5.6 mole creent vinylacetate in feed) Propylene 1 Because olefin polymers may contain bandsin the infra red which interfere with the carbonyl band, 5.8-5.85,meaningful infra red data must be in comparison with another sample ofthe resin e.g. oxidized vs. virgin (differential carbonyl absorbance).Hence carbonyl values in this table are given only for ethylenehomopolymers which are devoid of carbonyl or other interfering bands andhence give absolute carbonyl absorbance values.

Preferred means for oxidizing the olefin polymers are mechanical mixingapparatus open to the air such as two roll mills and closed intermeshinggear type apparatus provided with oxygen or air atmosphere. Theseapparatus especially when heated to between C. to C., depending upon theoxidation susceptibility of the polymer easily bring olefin polymersabove (1) the minimum peroxide content of 0.15 milligram peroxide pergram resin and into the preferred peroxide content range of from 0.60 to2.7 milligrams peroxide per gram resin; and (2) above the minimumdifferential carbonyl absorbance of 0.0005 per mil resin to withinpreferred range of 0.001 and above carbonyl absorbance per mil resin.Differential carbonyl absorbance per mil in the case of ethylenehomopolymer is equal to the absolute carbonyl absorbance due to theabsence of interfering bands in that polymer; with certain ethylenecopolymers, however, the differential carbonyl absorbance representsonly the relative amounts of carbonyl before and after the oxidationdescribed above.

An advantage of mechanical mixing apparatus is that polyisocyauate andperoxide reactants can be blended with the olefin polymer duringoxidizing or just subsequently thereto without the need of furtherhandling of the oxidized polymer. For example, an ethylene polymer canbe oxidized by milling 45 minutes at 170 C. in air and thepolyisocyanate and peroxide blended in by fluxing the polymer at 110 C.,adding the polyisocyanate and peroxide and milling for about 5 minutesor until the additive is uniformly dispersed. In addition to thepolyisocyanates and peroxides, there can be incorporated at this pointconventional additives, e.g. fillers such as carbon blacks and clays,pigments, catalysts for the isocyanate reaction e.g. dibutyl tindilaurate, and the like. Other means for incorporating the variousadditives and crosslinking agents can be employed. The latter can beadded during or after oxidation of olefin polymer.

As stated above, it is not necessary to oxidize olefin polymers prior toreaction with polyisocyanates in order to impart great adhesionabilityto the olefin polymer. There is an advantage, however, to pro-oxidizingthe olefin polymer prior to reaction with the polyisocyanates becausethe resulting adherent polymer is then also improved in other propertieswhich can be useful in a coating or bonding material as described above.

The virgin and oxidized olefin polymers are modified in the practice ofthis invention with organicpolyisodibenzylsulfonylethylenediamino-4,4'-diisocyanate 3,3'-dimeth0xy-4,4-diisoeyanate dibenzylsulfone4,4-methoxybenzylethylenedisulfone-3,3 '-diisocyanate4,4-methoxybenzylethylenediamino-3,3 '-diisocyanatel-methylbenzyl-2,4,6-triisocyanate1,3,5-trimethylbenzyl-2,4,6-triisocyanatenaphthalene-1,3,7-triisocyauate diphenylmethane-2,4,4-triisocyanate3-methyldiphenylmethane-4,6,4-triisocyanate4,4'-dimethyldiphenylmethane-2,2,5 ,5 '-tetraisocyanatetriphenylmethane4,4'-4"-triisocyanate, and.diphenyl-4,4'-diisocyanate-N-carbamyl acid chloride.

Preferred as the organic isocyanate cross-linking agents in thisinvention are the diisocyanates, particularly the aromatic diisocyanateswhere the -N=C O groups are on different ring carbon atoms of the sameor different aromatic ring, e.g., 2,4-toluene diisocyanate, dianisidinediisocyanate (3,3' dimethoxy 4,4 biphenylene diisocyanate), bitolylenediisocyanate, tolylene diisoeyanate, meta xylylene diisocyanate, andpolymethylene polyphenyl isocyanate.

The use of polyisooyanates with virgin olefin polymers in virtually anyconcentration is productive of adhesion ability and generally favorablemodification of polymer properties. The concentration of polyisocyanateshould not exceed, however, 40 percent by weight based on the virginolefin polymer as olefin polymer properties are lost to the composition.Conversely use of less than about 0.01 percent by weight polyisocyanatebased on the olefin polymer confers only negligible alteration of theolefin polymers. Above 0.25 percent by weight and particularly aboveabout .5 percent by weight of polyisocyanate based on the olefin polymerimparts significant property improvement. The improvement in olefinpolymer properties from about 0.5 to about 20 percent by weight ofpolyisocyanate based on the olefin polymer is not proportionatelyincreased by further increasing the polyisocyanate concentration tobetween 20 and 40 percent by weight. Hence, concentrations ofpolyisocyanate between 0.5 to 20 percent by weight are preferred. Aparticularly desirable balance of improved olefin polymer properties areachieved by the use of from about 3 to about of a polyisocyanate havingtwo N=C O groups and 1 to 6% of a polyisocyanate having three or moreN=@O groups based on the olefin polymer and, hence, this concentrationof these modifying agents is particularly preferred. By the termpolyisocyanate, mixtures of two or more polyisocyanates are meant to beincluded.

Among the modifications of olefin polymers caused by reaction withperoxides and the isocyanates in accordance with this invention, one ofthe most important is an increase in the gel content of the polymer.This property is a measure of the resistance to swelling of an olefinpolymer when in contact with solvents; and resistance to swelling is anindex to solvent resistance. Thus, as percent gel increases, solventresistance increases. The gel content is an index to other properties ofthe crosslinkcd olefin polymers also. For example, resins having greaterthan about 10% gel content are improved in clarity over uncrosslinkedolefin polymer, hence this amount of gel is highly desirable. For mostend-use applications a greater solvent resistance and higher molecularweight is desirable and the olefin polymer should have at least gelcontent. Also, higher gel content generally means greater stress crackresistance. On the other hand, the surprising adhesional characteristicsof the crosslinked polymers of this invention are apparent in resinscontaining no measurable gel content, i.e. 0% gel; this propertyimproves with increasing gel content.

The amount of gel formation is closely related to the degree ofoxidation. For example, gel appears only when a resin having a carbonylabsorbance per mil of above 0.0005 is reacted with a polyisocyanate; adoubling of carbonyl absorbance to 0.001 results in a sextupling ofpercent gel formation.

The practice of the present invention is illustrated by the followingexamples wherein all parts and percentages are by weight unlessotherwise specified.

Percent gel was determined by immersing a 0.3 gram piece of a 20 mil,cured, crosslinked plaque of olefin polymer enclosed in a mesh copperwire cage, in refluxing ethylbenzene for 16 hours. The cage and contentsafter this period were dried at C. for 3 hours. The weight of the resinin the cage divided by 0.3 and multiplied by 100 was the percent gel.

Clarity was empirically determined by looking through a 20 mil plaque.

Melt flow was determined according to ASTM D-123857T. As providedtherein, 1P melt flow refers to the decigrams of resin extruded in oneminute through a standard orifice at 190 C. and 44 pounds per squareinch pressure; 10P melt flow is the value found at 190 C. and 440 poundsper square inch pressure.

Carbonyl absorbance per mil was determined by infra red techniques usinga 20 mil plaque. Measurements were made at 5.84 microns and absorbanceper mil calculated according to the equation:

log

absorbance/mil:

where t=thickness in mils I =incident radiation, percent transmissionI=transmitted radiation, percent transmission Apparatus used was aPerkin-Elmer Model 21 double beam infra red spectrophotometer.

The carbonyl absorbance per mil of all olefin polymers except ethylenehomopolymers was measured as differential absorbance by placing anequally thick sample of virgin resin into the reference beam while theoxidized polymer sample was in the sample beam. Thus, the carbonylmeasured was that formed by the oxidation step.

Peroxide content was determined by weighing 0.500: 0.001 gram of finelydivided polyethylene (powdered to 20 mesh) into an 8 by 1 inch pressuretube; pipetting 25 ml. of alcohol-stabilized tetr-achloroethylene into a50 ml. graduate and adding 7 ml. of a one percent solution of sodiumiodide in methanol. This was mixed and added to the resin in thepressure tube which was then capped. Heat at 130 C. was applied for fiveminutes. The tubes were removed and cooled in Dry Ice for three minutes.Five milliliters of the methanol-iodine layer was pipetted off. Thetransmission was measured in a Beckman DU spectrophotometer at 450 and600 m using the methanol-iodide solution as a blank.

The sodium iodide in methanol was made up as follows: 1.00 gram ofsodium iodide was dissolved in 100 grams cc.) of distilled methanolwhich had been made acid by addition of a drop of phosphoric acid.

Peroxide content was then calculated from the formula:

X 100=c0rrected percent transmission at 450 mp A percent transmission at450 mg B=percent transmission at 600 my TABLE II.VARIATION' OF LIGHTTRANSMISSION WITH PEROXIDE CONTENT IN POLYETHYLENE Log of percent lightMilligrams peroxidic transmission (450 m oxygen/ gram resin Using thecorrected transmission from the above table for the milligrams ofperoxidic oxygen per gram resin, the peroxide content is calculated fromthe equation:

M/S=peroxide oxygen, mg. per gm. resin M =m-g. peroxidic oxygen fromchart S=sample weight Stress cracking resistance was measured asfollows:

A compression molded and cured polymer specimen 0.5 inch wide by 1.5inches long and 125 mils thick was slit 20 mils deep along its lengthfor 75 mils. The specimen was bent 180 and with 9 similar samples in achannel holder immersed in a non-ionic surfactant, nonyl phenoxypolyoxyethylene ethanol, at 50 C. Usually two channel holders were used,providing 20 specimens per test. Failure of a specimen was theappearance of a crack perpendicular to the slit. F is time of failure of10 samples of the 20 (i.e. 50% failure).

For convenience, 2,4-toluene diisocyanate is denoted by TDI anddianisidine diisocyanate by DADI.

Example l.Improvement in adhesion properties of virgin polyethylene byreacting with polyisocyanates Ethylene homopolymer having a density of0.92 and a melt index of 2.1, unoxidized, was mixed with 6% of adiisocy-anate by adding the diisocyanate to the ethylene homopolymerwhile being fluxed on a two roll mill. A 10 mil film was removed fromthe rolls and placed between a 20 mil thick sheet of polyethylene and asolvent washed, cold rolled steel panel. The assembly was placed betweencellophane wrapped polished platens and cured under 500 pounds/sq. in.at 170 C. for 10 minutes pressure in a standard hydraulic steam heatedpress.

The peel adhesion of the polyethylene film sheet to the substrate wasmeasured according to A-STM D-903 on a Scott tensile tester in thefollowing manner:

A one inch wide strip was cut across the polyethylene and down to thesubstrate. The strip wa then peeled from the substrate at a constantrate of one inch/minute and the force required measured in pounds/inch.

Results with two polyisocyanates are given in Table III below.

TABLE TIL-VIRGIN POLYETHYLENE REACIED WITH 1 Peroxide, mgJgm. 2 Carbonylabsorbancelmil.

Example 2.Impnovemen-t in adhesion properties of virginethylene/propylene copolymers by reacting with polyisocyanates Theprocedure of Example 1 was followed except that an ethylene/11%propylene copolymer was used in place of polyethylene.

Results are given in Table IV below.

TABLE IV.VIRGIN E'THYLENE/ ROPYLENE COPOLY MER AND POLYISOCYANATES PeelStrength (lbs/in.) Virgin Example Diisocyanate Percent 3 2A DADI 6 21 1Peroxide. mg./gm. 2 Carbonyl absorbance/mil.

Example 3.-Improvements in adhesion of virgin polyethylene to syntheticresin substrates by reacting with polyisocyanates The procedure ofExample 1 was followed except that The polyisocy-anate reactedpolyethylenes are improved in adhesion over virgin polyethylenes whichhave not been reacted with a polyisocyanate.

Examples 4-12.-Use of various polyisocyanates with virgin polyethyleneAdhesive properties were imparted to virgin polyethylenes by reactingwith Example Bitolylene diisocyanate 4 D'ian'isidine diisocyanate 5Mondur 1 6 m-Xylylene diisocyanate 7 Polymethylene polyphenyl isocyanate8 2,4-toluene diisocyan-ate 9 Nacconate 300 2 10a Nac-conate 310 3 "10b1 See Table VII.

2 Diphenyl methane-4,4 diisocyanate.

3,3'-clirnetl1yldiphenyl methane-4,4 dilsocyanate.

In each example, 6 parts of the polyisocyanate were milled ten endpasses at C. on a two roll mill with 94 parts of the virgin polyethylene(melt index 2.0, density 0.9196).

A 20 mil thick section was stripped off the mill .and compression moldedat 500 p.s.i. and 110 C. for 5 minutes. The sheet was then placedbetween two layers of stainless steel (35 mil Type 302) and the assemblywas placed in a press at C. and 500 p.s.i. for 5 minutes. Adhesion wasqualitatively tested immediately and .after immersing the test specimensfor 6 hours in boiling water. -In testing the panels were attempted tobe del-aminated by hand. Inseparable laminates were rated excellent;separable laminates were rated fair to poor or poor depending on theease of delamination. Results were as follows. A control, the sametreatment of the polyethylene without any polyisocyanate is also given.

TABLE VII Bond Strength Example Immediately After 6 hours/212 F.

Fair-Poor Poor Excellent Excellent Excellent Excellent ExcellentExcellent Excellent Excellent Excellent Excellent Excellent ExcellentExcellent Excellent Excellent Excellent Examples 11-l9.--Adhesion ofpolyisocyanate modified polyethylene to various substrates The olefinpolymer adhesive used was virgin polyeth ylene milled with 1% by weightdianisidine diisocyanate in the manner of Example 4. Laminates wereprepared as 1 1 in Example 4. All laminates formed were nondelaminableby hand pressure.

Example 11.35 mil stainless steel/ polyethylene/ 35 mil stainless steelExample:

111O mil copper/polyethylene/IO mil copper 12--3 mil aluminum/polyethylene/ 3 mil aluminum 13-40 mil GRS rubber/polyethylene/40 milGRS rubber 14-40 mil birch veneer plywood/polyethylene/40 mil birchveneer plywood 15-3 mil aluminum/l mil polyethylene/40 mil birch veneerplywood 16cotton cloth/ polyethylene/ cotton cloth 1720 mil polyethylenepolyethylene/ polyethylene 18-20 mil vinyl chloride-vinyl acetatecopolymer/ polyethylene/vinyl chloride-vinyl acetate copolymer19Portland cement block/polyethylene/portland cement block 1 Density0.916, melt index 20.

. Examples 2038 A number of olefin polymer polyisocyanate compositionswere prepared as in Example 4 and milled to a mil thickness. Thesesheets were then used to bond 20 mil virgin high density polyethylene(density 0.945, melt index 1.2) to stainless steel (35 mil Type 302).The laminates were prepared by placing the adhesive olefin polymer sheetbetween the polyethylene sheet and the steel panel and compression moldheating the assembly for 10 minutes at 170 C. and 500 psi. pressure.

Testing of adhesion was on a Scott tensile tester. Adhesion greater than40 psi. could not be measured since polyethylene fails at this pressure.Results and experimental data are summarized in the following table.

Examples 39-42.-Etfect of time and temperature on adhesive bond strengthExample 4 was duplicated but varying the bonding conditions to Example39, 120 C. for 2 minutes. Peel strength was 17 pounds/inch;

Example 40, 120 C. for 120 minutes. Peel strength was 39 pounds/inch;

Example 41, 170 C. for 10 minutes. Peel strength was pounds/inch;

Example 42, 200 C. for 2 minutes. Peel strength was over 40 pounds/inch.

Example 43 A polyethylene having a density of 0.916 and a melt index of2.1 is blended with 6 parts of 2,4-toluene diisocyanate per 94 parts byweight of the polyethylene in an extruder and the blend is extruded at160 C. onto aluminum foil to a thickness of one mil. Adhesion isexcellent.

Example 44 Polyethylene having a density of 0.920 and a melt index of2.1, 94 parts is dissolved in s-tetrachloroethane and 6 parts of2,4-toluene diisocyanate is added. The solution is coated onto stainlesssteel panels to a thickness of one mil cured at C. Adhesion isexcellent.

Example 45.-Adhesion of poly (butene-l) Example 15 aws duplicated butusing ninety-nine parts of poly(butene-1) and one part DADI. Thecomposition was sheeted and laminated between 3 mil aluminum foil and 40mil birch veneer. Testing was carried out as in Examples 4-10. Nodelamination by hand was possible.

TABLE VIII Polyiso- Steel-Polyethylene Laminate- Peel Strength Examplecyanate Percent Interlayer lbs in.

(ASTM D-903) Control I 0 1 20 H00 1-2 21- $4 12 22. 5 4 19 23. 35 24. 640 25. 20 40 26..-. V2 28 27. 1 40 28. 1 40 29. 1 40 30- 1 H (11 40Centre 1 31 mm-.. l g'lf gf g g gf Copolymer 0 Ethylene/Vinyl AcetateCopolymer, 2-3

5 2.2 Melt Index, 1.5 Mole percent vinyl 38 6 acetate in Feed. 40 0Ethylene/30% Vinyl Acetate Copoly- 5 mer. 1

0} High Density Polyethylene (1.6 Melt 1 1 Index, 0.964 Density). 29

0} Polypropylene(2.6 Melt Index 0.902 1 1 Density). 13

l 2,4-toluene diisocyanate.

2 Dianisidine diisocyanate.

Polymethylene polyphenyl isoeyanate. 4 Reaction product of one moletrimethylolpropanc, 3 moles toluene diisocyanate and 3 moles of phenol.5 Bitolylene diisocyanate.

Consideration of Table VIII reveals the wide range of olefin polymers,polyisocyanate concentrations, and polyisocyanates providing goodadhesives according to the present invention.

Example 46.-Adhesion of styrene polymer to polyethylene (density 0.95)Example 17 was duplicated but substituting as the inter- Example47.-Adhesion of styrene/propylene copolyrner to polyethylene (density0.95)

Example 46 was duplicated but using a styrene/propylene copolyrner inplace of the styrene polymer. No delamination by hand was possible.

As indicated above a further aspect of the present invention is theimprovement in physical properties of olefin polymers by the conjointuse of organic peroxides and polyisocyanates, which improvements are notassociated with drawbacks of peroxide crosslinking heretofore known inthe art and above mentioned. Importantly, there is a synergisticimprovement in the adhesional properties of olefin polymers usingorganic peroxides and polyisocyanates together, over either usedseparately.

In the compositions now being described the use of relatively lowamounts of polyisocyanate is quite possible and is in fact, preferred.In these compositions, from 0.25 to 40% by weight of the polyisocyanateis useful, but 0.25% to by weight of the polyisocyanate is ordinarilysufficient, and 0.5 to 6% is preferred, particularly 1 to 2%, incombination with from 0.25% to 3%, preferably from 0.5 to 2%, by weightof an organic peroxide.

The adhesional improvement is noted in both virgin and oxidized olefinpolymers. Solvent resistance and tensile strength of olefin polymers aswell as adhesion are improved when the polymers are oxidized to levelsabove described prior to reaction with the polyisocyanate and theperoxide.

The ratio of polyisocyanate and peroxide is not critical in thesecompositions. Generally the lower the amount of polyisocyanate, thehigher desirably is the peroxide concentration. Typical combinationsare:

Polyisocyanate, percent: Organic peroxide, percent Preferred levels ofoxidation in the olefin polymers for these compositions are:

Peroxide mg./gm 1.2-2.3 Carbonyl absorbence/mil 0.00l6-0.013

Organic peroxides useful in the present invention are, generally,compounds composed of carbon, hydrogen and oxygen, and have the generalformula R OOR wherein R is an organic radical and R is an organicradical or hydrogen. R and R can be hydrocarbon radicals or organicradicals substituted with a great variety of substitutents.

Preferred classes include alkyl peroxides e.g. t-butyl peroxide, alkylesters of organic per-acids e.g. t-butyl perbenzoate, and arylsubstituted alkyl peroxides e.g. dicumyl peroxide. Specific compoundsillustrative of these and other classes of organic peroxides are:

Cumene hydroperoxide Di-tert-butyl peroxide Dimethyl peroxide Tetralylhydroperoxide n-Octyl hydroperoxide Diethyl peroxide t-Butylhydroperoxide t-Butyl perbenzoate t-Butyl peracetate Peracetic acidDibenzoyl peroxide Bis(p-chlorobenzoyDperoxide Cyclohexanone peroxideDiacetyl peroxide Hyroxyheptyl peroxide Dibutryl peroxide Di-propionylperoxide Dioctanoyl peroxide 1 4 Dilauroyl peroxide Diisopropylperoxydicarbonate Bis(heptafiuorobutyryl) peroxide Bis(2,4-dichlorobenzoyl)peroxide p-Menthane hydroperoxide Pinanehydroperoxide Dicumyl peroxide Di-t-butyl diperphthalate t-Butylperoxyisobutyrate Methyl ethyl ketone peroxide2,5-dimethylhexane-2,S-dihydroperoxide and other organic peroxides suchas are well known to those in the art.

Examples 4849.Irnprovement in adhesion properties of oxidizedpolyethylene by reacting with polyisocyanates and organic peroxidesEthylene homopolymer having a density of 0.92 and a melt index of 2.1was oxidized and mixed with 0.5% of a diisocyanate (Control I), 0.5% ofa peroxide (Control II) and mixed with 0.5% of a diisocyanate and 0.5%of an organic peroxide (Examples 48 and 49), in the manner of Example 1.A 20 mil film was removed from the rolls and placed between a 20 milthick sheet of polyethylene and a solvent washed, cold rolled steelpanel. The assembly was placed between cellophane wrapped polishedplatens and cured under -200 pounds/sq. in. at C. for 10 minutes in astandard hydraulic steam heated press.

The peel adhesion of the polyethylene sheet was measured according toASTM D-903 in the manner of Example 1.

Results are given in Table IX below.

TABLE IX.-OXIDIZED POLYETHYLENE REACTED WITH POLYISOCYANATES ANDPEROXIDES Dicumyl Virgin Oxidized Example Diiso- Percent Peroxide,

cyanate percent 0. 04 l. 9

Control IA DADI. 0. 5 0 28-29 Control IB TDI 0. 5 10 35 Control 11. 0 0.5 8 Control III 0 0 3 DADL- 0. 5 0. 5 40 49- TDI 0.5 0.5 40

1 Sample milled 45 minutes in air at 170 C.

Example 50.Improvement in adhesion of virgin ethylene propylenecopolyrner by reacting with polyisocyanates and peroxides The procedureof Examples 48 and 49 was followed except that the ethylene/ propylenecopolymer of Example 2 was used, both as a virgin polymer and anoxidized polymer in place of the polyethylene.

Results are given in Table X below.

TABLE X.VIRGIN AND OXIDIZED ETHYLENE/PROPYL' 1 Sample milled in air 45minutes at 170 C. 2 Peroxide, mgJgrn. 3 Carbonyl absorbancelmil.

Examples 5152.Adhesion of polyisocyanate and peroxide modifiedpolyethlene to various substrates The procedure of Examples 48 and 49was followed except that Mylar and nylon were used as substrates inplace of cold rolled steel panels.

Results are given in Table XI.

TABLE XL-OXIDIZED POLYETHYLENE AND POLY- ISOCYANATE AND PEROXIDE PeelStrength Sub- Pcroxido Carbonyl Diiso- Dicumyl strata Content,Absorbanec cyanato, Peroxide, Example mg./ gm. per mil Percent PercentMylar Nylon film (5 film (20 mil) mil) 2.2 0. 00s 0 1 2.2 0. 00s 0 0 2.20.008 e 1 2.2 0. 00s 2.2 0. 00s 0 l 2.2 0. 00s 6 0 Example 52..-" 2. 20. 00s 6 1 As further broadly pointed out above olefin polymers PercentGel: C ntaining hydroxyl (-OH) groups in their structures Before 0 rcrosslinked to advantage by polyisocyanates. Specifical- After 79lyirirlrliprovtementts 1aretosbotained in tsuch olifin polymers Example54 w to con am a eas percen y weig or a cornbined alphamonoethylenically unsaturated hydrocarbon mp 53 was duplicated but using3% of DADI- having from 2 to 4 carbon atoms, inclusive, preferably 30Propfirtles were: ethylene and up to 50 percent by weight of one or twoFlaw Index; monomers copolymerizable with ethylene and which con- B f139 win an hydroxyl group. These olefin polymers suitably Aft 0 have amelt index (ASTM 123857T) in the range of 0 G to 1000 and preferably inthe range of 0.02 to 100 deci- Percent e grams/minute. Examples of theolefin polymers, illustra- Before 0 tive of the class are:ethylene/formaldehyde copolymers; After 72 hydrolyzed ethylene/vinylformate copolymers; hydro- Emmple 55 lyzed ethylene/vinyl acetatecopolymers; and terpolymers 3O of similar comonomers, all containing aminimum of 50 percent combined ethylene, propylene or butene-l. Thesehydroxyl containing olefin polymers contain from 0.5 to 21 percent byweight hydroxyl groups and preferably from 1 to 10 percent by Weighthydroxyl groups.

The improvements obtained in these olefin polymers by modification withpolyisocyanates are in many respects similar to improvements obtained inthe hereinabove described olefin polymer e.g. increased adhesionability,improved solvent resistance and clarity, excellent stress crackresistance, increased molecular weight, improved tensile properties andimpact strength.

In the hydroxyl containing olefin polymer compositions now beingdescribed, the concentration of polyisocyanate is suitable within thelimits set out above and is preferably in the range of 0.01 to 30 parts,particularly from 1 to parts of the polyisocyanate per 100 parts of thehydroxyl containing olefin polymer.

In the following examples the hydroxyl containing olefin polymer wasfiuxed on a two-roll mill at about 110 0, except that olefin polymerscontaining 6 and 15 percent by weight hydroxyl groups were milled at 50C. The polyisocyanate was milled in for about 10 minlutes, including 10end passes to assure complete dispersion of the additive. Compressionmolded plaques mils thick) were prepared by curing at a temperature andfor a time indicated in each example.

The various hydroxyl containing olefin polymers were prepared bydirectly polymerizing ethylene with an hydroxyl group containingmonomer, such as formaldehyde or by complete or partial hydrolysis of acopolymer of ethylene and an ester e.g. ethylene/ vinyl acetatecopolymer hydrolyzed or ethylene/ vinyl formate copolymer hydrolyzed.

Example 5 3 An ethylene/vinyl formate copolymer having a melt index of9.7 and a density of 0.950 was hydrolyzed to an hydroxyl content of 1.5percent by weight and modified with 3 percent TDI. Cure was at 150 C.for 60 minutes. Properties of the copolymer before and aftermodification were as follows.

Flow Index:

Before 1 3 9 After 0 Example 53 was duplicated but using 6% of aphenolblocked polyisocyanate (Mondur S) and an ethylene/ 24% vinylacetate copolymer partially hydrolyzed to an hydroxyl content of 3.2percent by weight. Cure was at 180 C. for minutes. Properties were:

Flow Index:

Before 200 After 25 Percent Gel: Before 0 After 54 Examples 56-59Example 53 was duplicated but using various amounts of TDI. Results aresummarized in Table XII.

TABLE XII Percent Flow Index Percent Gel Example TDI Before After BeforeAfter 0. 01 139 116 0 0.1 139 20 0 ll 1 130 0 0 e4 10 139 0 0 90 Example60 Example 53 was duplicated but using 10% TDI and curing at 100 C. for5 minutes. Flow index was reduced from 139 to 0; percent gel was 77%.

Example 61 Example 62 Example 61 was duplicated but using an ethyleno/10.1% vinyl acetate copolymer hydrolyzed to 2.1% hydroxyl content and 6%Mondur S. Flow index was reduced from 298 to 0; percent gel was 73%;tensile impact was increased from 184 foot-lbs./cubic in. to 737 75foot-lbs./cubic in.

1 7 Example 63 Example 61 was duplicated but using the ethylene/ vinylformate copolymer of Example 5 3. Flow index was reduced from 139 topercent gel was 79% stress cracking resistance (F was increased from 0.1hour to over 500 hours, and cloudiness was changed to clarity.

Example 64 Example 3 was duplicated but using an ethylene/ vinyl formatecopolymer completely hydrolyzed to an hydroxyl content of 0.5 percent.Flow index was reduced from 112 to 0; percent gel was 41%.

Example 65 Example 53 was duplicated but using an ethylene/formaldehydecopolymer having a melt index of 10,000 and containing 5% by weighthydroxyl groups and 1% of TDI. Flow index was reduced from 200 to 0;percent gel was 91%.

Example 66 Example 65 was duplicated but using an ethylene/formaldehydecopolymer having a melt index of 10,000 and containing 14% by weighthydroxyl groups. Flow index was reduced from 200 to 0; percent gel was75%.

Example 67 Example 65 was duplicated but using an ethylene/formaldehydecopolymer'having a density of 0.931, a melt index of 15 and having anhydroxyl content of 1%. Gel was increased to 81% I claim:

1. Adhesive consisting of the reaction product of (1) virgin olefinpolymers selected from the group consisting of (a) virgin olefinhomopolymers of monoethylenically unsaturated hydrocarbons, (b) virginolefin copolymers of a monoethylenically unsaturated hydrocarbon and acompound selected from the group consisting of carbon monoxide, styrene,vinyl stearate, butene, vinyl acetate, vinyl formate, methyl acrylate,Z-ethyl hexyl acrylate, N- methyl-N-vinyl acetamide, ethyl acrylate,isoprene, butadiene, acrylarnide, vinyl triethoxysilane, bicycloheptene,bicycloheptadiene and divinyl phosphonate, and (0) Virgin olefincopolymers of at least two difierent monoethylenically unsaturatedhydrocarbons and (2) from 0.01 to 40% by weight based on the weight ofthe virgin olefin polymer of an organic isocyanate having at least two-NCO groups.

2. Adhesive of claim 1 wherein said virgin olefin polymer ispolyethylene.

3. Adhesive of claim 1 wherein said virgin olefin polymer is anethylene-propylene copolymer.

4. Adhesive of claim 1 wherein said virgin olefin polymer is anethylene-vinyl acetate copolymer.

5. Adhesive of claim 1 wherein said virgin olefin polymer ispolypropylene.

6. Adhesive consisting of the reaction product of (1) an olefin polymerselected from the group consisting of (a) virgin olefin homopolymers ofmonoethylenically unsaturated hydrocarbons. (b) virgin olefincopolymersof a monoethylenically unsaturated hydrocarbon and a compound selectedfrom the group consisting of carbon monoxide, styrene, vinyl stearate,butene, vinyl acetate, vinyl formate, methyl acrylate, Z-ethyl hexylacrylate, N- methyl-N-vinyl acetamide, ethyl acrylate, isoprene,butadiene, acrylamide, vinyl triethoxysilane, bicycloheptene,bicycloheptadiene and divinyl phosphonate. (c) virgin olefin copolymersof at least two diiferent monoethyleni cally unsaturated hydrocarbons,(d) oxidized olefin polymers having a peroxide content of from 0.15 to3.5 milligrams per gram resin and containing at least 10 percent byweight of a monoethylenically unsaturated hydrocarbon containing from: 2to 4 carbon atoms inclusive, and (2) from 0.01 to 40% by weight based onthe weight of the olefin polymer of an organic isocyanate having atleast two NCO groups and (3) from 0.25 to 3% by weight based on theweight of the olefin polymer of an organic peroxide.

7. Adhesive of claim 6 wherein said olefin polymer is polyethylene.

8. Adhesive of claim 6 wherein said olefin polymer is anethylene-propylene copolymer.

9. Adhesive of claim 6 wherein said virgin olefin polymer ispolypropylene.

References Cited UNITED STATES PATENTS 2,565,783 8/1951 Sehouteden26077.5 2,690,780 10/1954 Cousins 260-77.5 2,826,570 3/1958 Ivett 2607752,833,740 5/1958 Verbanc 26063 2,839,478 6/1958 Wilms et a1. 260253,027,343 3/1962 Kane 26077.5 3,171,830 3/1965 Kehr 26O88.2 3,179,7164/1965 Bruin et al. 260878 3,210,323 10/1965 Bush et al. 26077.53,225,119 12/1965 Baker 260874 3,228,793 1/1966 Stemmer et al 26077.53,234,197 2/1966 Baum 26093.7 3,296,210 l/1967 Wilson et al. 260733,317,477 5/1967 Wilson et al. 260-73 2,373,561 4/1945 Hanford 26067FOREIGN PATENTS 581,279 10/ 1946 Great Britain.

OTHER REFERENCES Renfrew, Polythene 1960), pages 390-391 relied upon.Angewandte Chemie, volume 73, Number 6 (Mar. 21, 1961), pages 177-186relied upon.

DONALD E. CZAJA, Primary Examiner.

F. MCKELVEY, M. C. JACOBS, Assistant Examiners.

